In usual serum examinations, blood collected into a blood collection tube is caused to coagulate, and then centrifuged for separating an intended blood component.
Such a blood collection tube desirably has blood coagulation promoting ability that allows the collected blood to coagulate in short time, and blood clot detaching ability that prevents the coagulated blood from adhering to the inner wall of the blood collection tube in the form of blood clots while detaching adhered blood clots. As such a blood collection tube, blood collection tubes whose inner wall is processed in various manners have been reported.
For example, Japanese Examined Patent Publication HEI-5-10095 discloses a blood collection tube in which an inner wall of a vessel made of a specific material is coated with a blood coagulation promoter comprising a water-insoluble silicone oil, polyvinylpyrrolidone and an adsorptive inorganic substance.
Japanese Unexamined Patent Publication HEI 5-103772 discloses a blood collection tube in which an inner wall of a vessel made of a specific material is coated with a blood coagulation promoter via a water-soluble silicone oil.
These reported that coating the inner wall of a blood collection tube with the coagulation promoter as described above enables the collected blood to coagulate in short time and prevents blood clots from adhering to the inner wall of the tube.
However, in such a blood collection tubes, it was necessary to apply the silicone oil in high concentration so as to prevent blood clots from adhering to the inner wall of the tube. To be more specific, concentration of the silicone oil to be applied to the inner wall of the blood collection tube was as high as 5.0×10−6 to 1.0×10−5 g/cm2. This led the problem that the presence of silicone oil at high concentration may adversely affect test values.
Another problem was that when these blood collection tubes have a plug member, blood clots come into adhered to the plug member upon coagulation of the blood collected into the blood collection tube.